Apparatus for spray drying milk and the like

ABSTRACT

A method of spray drying and apparatus therefor in which milk and the like is sprayed and dried chiefly with hot air. The liquid to be dried is sprayed by means of a single pressure spray nozzle disposed in the upper portion of a drying tower into which hot air is also introduced. The liquid sprayed proceeds downward with the hot air and falls, after being substantially dried, into a zone of cool air provided in the lower portion of the tower where complete drying as well as cooling takes place. The hot air issuing from the upper portion of the tower in the downward direction encounters dry cooling air supplied from the lower portion of the tower about midway in the tower and they are exhausted from the side of the tower.

United States Patent [72] Inventors Katsuto Okada Tokyo; Fumio Kato, Kawasaki-shi, both of, Japan [211 App]. Nov 820,920 [22] Filed May 1, 1969 [45] Patented Aug. 3, 1971 (73] Assignee Morinaga Nyugryo Kabushlki Kaisha Tokyo, Japan [32] Priority May 6, 1968 [3 3] Japan [31 43/30199 [S4] APPARATUS FOR SPRAY DRYING MILK AND THE LIKE 4 Claims, 1 Drawing Fig.

[52] US. Cl. 159/4, I 99/203 [51] Int. Cl 801d l/16, BOld 1/00, A22c H00 [50] Field 01 Search l59/4,4B, 4 C, 4 CC, 4 D, 4 R,-4 MS, 4 VMS, 48; 99/200, 203

[5 6] References Cited UNITED STATES PATENTS 1 ,632,959 Gartner 260/644 Primary Examiner-Norman Yudkoff Assista m Examiner.l. Sofer Attorney- Kurt Kelman ABSTRACT: A method of spray drying and apparatus therefor in which milk and the like is sprayed and dried chiefly with hot air. The liquid to be dried is sprayed by means of a single pressure spray nozzle disposed in the upper portion of a drying tower into which hot air is also introduced. The liquid sprayed proceeds downward with the hot air and falls, after being substantially dried, into a zone of cool air provided in the lower portion of the tower where complete drying as well as cooling takes placev The hot air issuing from the upper portion of the tower in the downward direction encounters dry cooling air supplied from the lower portion of the tower about midway in the tower and they are exhausted from the side of the tower.

eewnzn REGEPTAQLE Patented Aug. 3, 1911 HEATER EXHAUST v 50% MILK SOLIDS POWDER RECEPTACLE INVENTORS kATsuTo 0KM A =FUM|O l (A TO APPARATUS FOR SPRAY DRYING MILK AND THE LIKE The present invention relates to a method and apparatus therefor wherein liquids containing substances which are to be concentrated, dried and solidified, particularly milk is sprayed into hot air and dried.

Spray driers have hitherto been employed in the manufacture of powdered products, such as dry milk and others. Among the machines of this kind capable of producing high quality powdered products, a normal room temperature drier has been considered as the most desirable. However, it is usual for such a spray drier to require a huge drying tower. A drying tower, about 70m in height and about 16m in diameter will be required, for example, to handle concentrated milk containing about 50 percent by weight of solid matter at the rate of about 2,000 kg. per hour, and moreover such milk must be sprayed by 6 to 12 spray nozzles disposed at the upper end of the tower under a pressure of about 150 kgJcm. But this cold or normal room temperature spray-drying method. is disadvantageous in that although generally high quality products are obtainable the range of humidity and temperature in the drying chamber allows multiplication of micro-organisms, and, the use of a number of spray nozzles involves some dm'rcuity in providing uniform spraying.

n the other hand, processes or apparatus have been proposed in which spray-drying is effected employing hot air. In the manufacture of synthetic detergents, for example, attempts have been made to spray liquids against hot air issuing from the opposite direction. Such attempts are disadvantageous, however, in that as the liquid is dried, it passes through higher temperature and hence drier atmospheres with the result that the quality of product obtained is deteriorated owing to overheating. Another attempt to feed hot air in the same direction as the direction of movement of sprayed tine liquid particles has a drawback in that the hot air supplied must be unnecessarily high in temperature as it must provide a dehumidifying atmosphere which allows the sprayed liquid to produce completely dried powder and therefore the liquid is subjected to sudden heating where the fine liquid particles encounter the hot air. This also deteriorates the quality of the product obtained. Another drawback accompanying such hitherto practiced methods of hot air drying is the formation of aggregated particles in the dry milk obtained. The reason is that the dried falling powder milk flakes are heated above the solidification temperature of the fats contained therein so that they tend to stick to the inner wall of the lower conical section in the drying tower or to the sides of a product-packing device and to form there dried layers which fall into and become mixed in the product. The powder milk flakes adhering to the sides of the conical section deteriorate because they are exposed to hot air for a long time and become overheated. it is self-evident that such phenomenon make these prior art machines unsuitable especially as driers for drying milk.

According to the present invention, a spray-drying tower is provided in which the upper and lower portions have a heating section and a cooling section, respectively. A liquid to be dried is caused to pass through the tower. thus producing a good quality dry powdered product.

On the other hand, it has been accepted that there is a cer= rain limit to the amount of liquid which a single pressure spray nozzle can emit. although it is desirable to increase the amount of liquid treated in a single drying tower in order to cf ficiently carry out the sprsy drying procedure. Such being the case, it has been a usual practice to mount as many as 6 to 12 pressure nozzles in one drying tower. However, with a number of pressure spray nozzles used. it has been diificult to cause all the nozzles to emit a spray of uniformly fine particles. Com sequently. in order to attain thorough drying of larger liquid particles. an atmosphere must tie-provided which would be too hot for smaller liquid particles. Thus. it has been impossible to produce quality powder products.

As a solution for this problem, it has been found that by em- I ploying a disk atomizer. the amount of liquid to be sprayed could be increased as compared to a pressure nozzle. How ever, the spray angle of a disk atomizer is too large. Thus, this kind of atomizer is disadvantageous in that it tends to cause the falling liquid particles to scatter within the drying tower and stick to the wall thereof requiring that the diameter of the tower be made larger.

Accordingly, the present invention further provides a method and apparatus therefor wherein a liquid is efficiently emitted from a single prepsure nozzle with a coefficient of discharge the value of which is smaller than those of the normally workable coefficients of discharge, whereby the sprayed liquid falls within a drying tower with hot air flowing in the same direction as the liquid so that it turns into nearly dried powder form and continues to fall further in this nearly dried powder form as it passes through a section of cooled and dehumidified air supplied at the bottom portion of the tower in order that the nearly dried powder can be completely dried and cooled. Thus, not only does the present invention make it possible, through the use of hot air drying, to handle the same amount of liquids as the conventional normal temperature driers with a much smaller apparatus, but it also prevents dried powder materials from being subjected to excessive heating and from sticking to form a layer thereof on the wall of a funnel or conical shaped section in the lower part of the tower because drying takes place in the cold air section unlike in the conventional methods of hot air drying. It is to be noted here that there is a distinct boundary surface between aheating section formed by heated or hot air in the upper portion of the tower and a cooling section formed by cooled and dehumidiiied air in the lower portion of the tower owing to the difference between the specific gravity of the two sections. This boundary surface is maintained because the humid hot air and the warmed cold air are discharged from the extension of the boundary surface. Entralned with the discharged mixture of hot and cold air from the boundary surface. some of the dried powders are also discharged from the tower. However. the discharged powder can be separated from the mixture. as for example, by a cyclone separator and recirculated to be returned to the cold air section.

As is evident from the foregoing, an object of the present invention is to provide a method of spray=drying and apparatus therefor capable of manufacturing quality powder products in a highly efficient continuous manner with inexpensive equipment.

Another object of the present invention is to provide a spray'drying apparatus capable of performing a highly efficient spraying procedure wherein the liquid which has hitherto been disposed of by a plurality of pressure nozzles is shot out by a single pressure nozzle under practically the same pressure as heretofor used. but with an extremely low coefficient of discharge.

A further object of the present invention is to provide a method of spray drying wherein the spraying characteristics are easily controlled with the use of a single pressure nozzle to thereby produce good quality products.

A still further object of the present invention is to provide a method of spray drying and apparatus therefore wherein powders heated and dried with hot air are fully and completely dried and cooled by passing them through cooled and dehumidlfied air so that powder products are obtainable which can be readily packed into containers without forming any agglorneration or lumps.

A still further object of the present invention is to provide a method of producing dry powders and apparatus therefor wherein a sprayliquld is passed through both a heating section and a cooling section to produce dry powders.

A still further object of the present invention is to provide a method at hot air spray drying and apparatus therefor wherein dry powders falling into a funnel or conical shaped part in the lower portion of a drying tower are cooled such that the dried powders arriving at said tunnel or conical part are not permitted to stick to and form a layer on thefunnel or conical shaped-part.

A still further object of the present invention is to provide a method of hot air spray-drying and apparatus therefor wherein a funnel or conical shaped part in the lower portion of a drying tower is cooled such that no dried powders are permitted to stick to and accumulate on the sides of said conical part.

A still further object of the present invention is to provide a method of hot air spray drying and apparatus therefor wherein there are provided a heating section in the upper portion of a drying tower and a cooling section in the lower portion of the tower with a sprayed liquid falling through both said sections, in order that a boundary layer is maintained between said two sections both heating and cooling gaseous bodies existing in the interfacial section are discharged from the tower through said boundary layer, and dried powders entrained with the discharged gaseous bodies are separated to be recirculated back into said cooling section.

The foregoing and other objects as well as characteristic features of the present invention will be apparent with reference to the following description of the invention made in conjunction with the accompanying drawing.

The accompanying drawing shows, by means of a schematic diagram, an embodiment of a hot air spray-drying apparatus according to the present invention.

Referring to the drawing, a drying tower 1 consists of an upper cylindrical part 2 and a lower funnel or conical shaped part 3. Mounted in the central inner upper portion of the tower 1 is a nozzle 4 to which is fed concentrated milk of up to about 50 percent by weight concentration from a feed pump 5 through a conduit 6. Also connected to the top'of the tower l is a conduit 8 extending from a source 7 of hot air supply including a filter, a blower and a heat exchanger for heating purpose. Hot air is thus fed into the tower through the conduit 8.

Disposed at the bottom end of the lower funnel shaped part 3 of the tower l is a port 9 through which dried milk powder is discharged to a means l9 which receives the discharged product. First and second cold air feed ducts l0 and 10' are provided within the funnel shaped part 3 immediately above the discharge port 9. The ducts to and 10' are respectively connected to conduit: 12 and 12' from a source 11 of cold air supply including a filter. a blower and a heat exchanger for dehumidification.

An exhaust duct 13 is disposed at the junction of the cylindrical part 2 and the funnel shaped part 3 and a conduit 14 provides a connection between a cyclone l5 and the duct 13. The cyclone i5 is provided with an exhauster l6 and a powder discharge port I? which opens into a powder recovery conduit 18. The conduit 18 is connected to the cold air supply source 11 and the duct 10, for example.

Within the tower 1, hot air at about 150" C., for example, flows downwards in the direction shown by arrows A, while dehumidified cold air at about 15. to 20 (2., for example, goes up within the tower in the direction shown by arrows B. The two air streams form interface D and are exhausted at 13. as shown by arrow C. The velocity of those current streams is low, such as in the order of lm/sec. Because of the difference between the specific gravity of the hot and cold air and of the slow but continuous supply thereof, the hot and cold air are separated from each other forming the interface D thcrcbetwecn.

Milk normally concentrated up to about 50 percent conccn trstion is sprayed into the tower 1 from the nozzle 4 by the pressure pump 5. The fine particles of the sprayed conccm trstcd milk fall within the tower 1 in the manner shown by an arrow B, through the heating section and then through the cooling section, to the product discharge port 9, during which the army of concentrated milk is subjected to the drying and cool ng.

The nozzle 4 is not s centrifugal atomizer. but a high pres sure nozzle. The centrifugal atomizer has a large or horizontal spray angle. and a single unit can spray a large amount of liquid in a short time. This means that even it a sufficiently large diameter drying tower is used, a spray of milk will still moisten the tower wall. forming thereon a sticking layer of solidified milk. Naturally, there is a limit to the range of discharge coefficients of pressure nozzles which any persons skilled in the art consider as practicable range from a common sense point of view. However, with the apparatus according to the present invention, spraying is effected under high pressure and with a lower coefiicient of discharge. Although spraying under such conditions may be accompanied by some variation in the particle size distribution of sprayed liquid particles thus obtained as compared to that obtainable with the usual coefficients of discharge, such particles may be uniformly dried in the apparatus of the present invention. Thus. by effecting the spraying procedure in this way. it has been possible to multiply efficiency about tenfold with the use of only a single nozzle as compared with the hitherto employed apparatus in which, for example, 6 to 12 nozzles have been utilized.

As sprayed by the nozzle 4, the concentrated milk is scattered by a relatively small spray angle and falls, entrained by the hot air. within the cylindrical part 2 of the tower. The sprayed fine particles of milk reach the interface D within 2 or 3 seconds and at an almost dried state. The dry powder thus arriving at the interface contains molten fat and has a very low water content, thus tending to agglomerate into a lump. The powder which is almost dry when arriving at the interface D continues to fall further and enters into a cooling section in the funnel shaped part 3 where its moisture content is removed and the fat solidified in a dry atmosphere resulting in a thoroughly dried powder. The thoroughly dried powders falls along the wall of the tower to its lower part where the powder is accumulated. Cooled and dehumidificd air is blown from the duct 10 through the accumulated dry powder so that the powder is further kept thoroughly dried and cooled.

The moist hot air entering from the top of the drying tower and arriving at the interface D combines with the rising cold air from the ducts 1.0 and 10'. to reach the cyclone 15 from which the combined air is discharged into the atmosphere by the exhauster 16. Carried by the exhausted air current from the tower 1. some of the almost dried powders are also discharged from the tower. However, these powders are recovered by the cyclone 15 and. carried by the air current in the conduit 18. are returned into the drying tower 1. The lower end of conduit 18 may be connected to the cold air feed means ll or it may be connected directly to a blower adapted to supply atmosphere under pressure.

The thoroughly dried and cooled powders which are accumulated in the lower portion of the. tower are discharged into a container 19 or to a product conveying means.

The outline of a test plant of the. apparatus illustrated herein is shown below and the product obtained has been in no way inferior to those obtained from the hitherto used normal temperature drying machines:

Drying tower; Height of cylindrical part lSm. Diameter of cylindrical part 5.5m. Height of conical shaped part 6.5m.

Pressure nozzle: Number of nozslc 1 Pressure applied l'iOlrg/cm'. Spray capacity 5.000kg./hr. Size of psrlicls 140 15 Temperature of hot air injected L 0 (2. Temperature of cold air injected 20 C. (50 percent R.H.) Tcmpsrature otintennsdiary exhausted nlr lid-8ST.

in this tcst plant apparatus, the spray angle of the fine particles emitted by the nozzle was about and the diameter of particles was relatively settled in spite of the extremely low coefficient of discharge. The time required for the particles, carried by the hot air. to reach the interface was 2-3 seconds. while the amount of powders exhausted out of the drying tower together with the air current through the exhaust duct was in the order of 20 percent. But the thus exhausted powder millt was separated in the cyclone and recirculated into the tower with the cold air. The powder milk arriving at the conical-shaped part fell smoothly along the inner wall of the tower without any formation of lumps and there was no formation of 5 deteriorated powder milk or lumped powders. Moreover, solubility of the product obtained was excellent and wettability was also equal to that of the products obtained from the cold-drying process.

From the foregoing it is evident that according to the present invention quality dry powders are obtainable with a high rate of yield. In addition, no adhesion of solid particles to the wall of the drying tower is permitted while in operation and smooth control of the amount of spray is also ensured.

Although the illustrated embodiment of the present invention has been explained referring, by way of an example, to the manufacture of dry milk, it is apparent that the present invention is also applicable to the manufacture of other powder products. It will be evident to those skilled in the art that the method and apparatus according to the present invention are not limited to those described hereinbefore and many modifications or changes may be made thereto within the scope and spirit of the present invention.

I claim:

1. A spray-drying apparatus for milk and the like, comprising a drying tower consisting of a cylindrical upper portion and an inverted conical lower portion, hot air feeding means connected to the upper portion of said tower to supply hot air into said drying tower, dry cold air feeding means connected to the lower portion of said drying tower to supply dehumidified cold air into said tower, said cold air feeding means including separate branch conduits for supplying said cold air at upper and lower levels of the tower wall in said inverted conical portion, means disposed at the junction of said cylindrical portion and said inverted conical portion where said supplies of hot and cold air contact each other in said drying tower to exhaust the blended air of said hot and cold airs from said tower, a pressure spray nozzle mounted in the upper portion of said tower, a discharging port for a dry powder product disposed in the lower portion of said tower, and circulating means for returning the powder discharged through said exhausting means into the lower portion of said tower.

2. A spray-drying apparatus according to claim 1, wherein said pressure spray nozzle is a single-high-pressure nozzle for spraying the milk or the like with a low coefficient of discharge.

3. A spray-drying apparatus according to claim 1, wherein the circulating means includes a cyclone separating the powder and returning the same to the lower tower portion, the air being exhausted from the cyclone to the atmosphere.

4. A spray-drying apparatus according to claim 3, wherein the powder separated in said cyclone is fed to the cold air feeding means. 

2. A spray-drying apparatus according to claim 1, wherein said pressure spray nozzle is a single-high-pressure nozzle for spraying the milk or the like with a low coefficient of discharge.
 3. A spray-drying apparatus according to claim 1, wherein the circulating means includes a cyclone separating the powder and returning the same to the lower tower portion, the air being exhausted from the cyclone to the atmosphere.
 4. A spray-drying apparatus according to claim 3, wherein the powder separated in said cyclone is fed to the cold air feeding means. 